The present invention relates to a mechanical seal capable of providing a good sealing function by the engagement of a seat ring in sliding contact with a follower ring.
In general, a mechanical seal for a water pump used in an automobile engine includes a follower ring secured to a housing in such a manner as to allow a rotary shaft to pass through the ring, and a seat ring rotatable with the rotary shaft and in sliding contact with the follower ring. With this arrangement, fluid is prevented from leaking from the outside of an assembly toward the radially inner side, i.e., toward the rotary shaft, by the sliding contact provided between the follower ring and the seat ring.
Conventional mechanical seals formed with fine grooves at sliding contact portions have been described in U.S. Pat. No. 4,099,729.
In another seal, as shown in FIG. 1, fine grooves 31 are formed on at least one of the contracting surfaces of the follower and seat rings with the grooves being closed at their radially outer ends and opened at their inner ends. The outer ends of the grooves 31 are inclined to the rear side with respect to the relative direction of rotation between the follower and the seat rings. Such a structure is shown in commonly assigned copending U.S. patent application Ser. No. 642,733.
A mechanical seal of this type provided with fine grooves 31 is advantageous in attaining a better sealing effect than the conventional mechanical seal. However, such mechanical seal when employed in a water pump for an automobile results in increased frictional torque, even though contact with area between the rings is reduced by the area of the fine grooves.
Various experiments were conducted to find the reasons for such increased frictional torque. It is found that the mechanical seal for the water pump uses water as a lubricant normally at a temperature of more than 80.degree. C. Therefore, the sliding surfaces are subjected to a temperature higher than the water temperature so that a sharp corner 33, defined by each of radially inner end portions of the fine grooves 31 and an inner circumferential surface 32 at the opening end of the grooves 31, is susceptible to deformation due to heat. The thermally deformed acute angle portion 33 is solidified. Due to its contact with the opposing surface, the frictional torque is increased.